Answer by Ian Bush for Why must there be degeneracy in the orbitals to have a...
In the abstract to the original Jahn-Teller paper it is stated:[1]We shall show that stability and degeneracy are not possible simultaneously unless the molecule is a linear one.Thus the Jahn-Teller...
View ArticleAnswer by Ian Bush for Kinetic Energy Evaluation Integral Evaluation Program
The equation for the Kinetic Energy matrix element that you quote is for two unnormalised 1s Gaussians. The d factors contain the normalisation factors and the contraction coefficients - look more...
View ArticleAnswer by Ian Bush for Kinetic Energy Evaluation Integral Evaluation Program...
TAR86 gives the correct mathematical answer, but given how you express yourself I thought I would try and explain it at a slightly lower level.Your problem is in the sentence "I understand T11 to be...
View ArticleAnswer by Ian Bush for Would there be need for periodic DFT if we are able to...
Quoting from the article The ReaxFF reactive force-field: development, applications and future directions"Such empirical methods, including reactive force-field (ReaxFF),1 trade accuracy for lower...
View ArticleAnswer by Ian Bush for Proof for second-order perturbation term of energy
As the unperturbed Hamiltonian is Hermitian it follows that$$\int{ψ^{(0)*}_0}\hat {H}^{(0)}{ψ^{(2)}_0} dτ = \left[\int{ψ^{(2)*}_0}\hat {H}^{(0)}{ψ^{(0)}_0}...
View ArticleAnswer by Ian Bush for Why is oxygen more stable than oxygen dication?
You have to consider the system as a whole - you can't directly compare $\ce{O_2}$ and $\ce{O_2^2+}$ because they have different numbers of particles. To put it another way when you consider the...
View ArticleAnswer by Ian Bush for Long-lived, non-lethal radioisotope for fiction
One possibility is Technetium-99m . According to wikipedia it is the most commonly used medical radioisotope in the world, so get your person involved in an appropriate medical procedure and you should...
View ArticleAnswer by Ian Bush for Normalization of a free particle in 1 dimension
To answer the question, over and above the errors noted in the other answer the integral is just not well defined - it is infinite. There are two ways to see thisThe "common sense" method. Consider$$...
View ArticleAnswer by Ian Bush for Molecular orbitals in an ionic diatomic compound
As$$\gamma = \dfrac{c_A}{c_B}$$when $c_A=0$, $\gamma$must also be zero. This follows as $c_B$ can not be also be zero as the wavefunction is normalised to unity. Thus under such conditions it is...
View ArticleAnswer by Ian Bush for Why are MD simulations necessary for obtaining...
In principle you can, assuming you are given $V(\{\bf{r_i}\})$ where $\{\bf {r_i} \}$ is the set of variables that define a configuration in the system - this is typically the coordinates of the atoms,...
View ArticleAnswer by Ian Bush for On the definition of eigenframe
I can't find anything definitive but bothhttps://www.thestudentroom.co.uk/showthread.php?t=4172326andhttps://www.physicsforums.com/threads/eigenframe-definition-please.876035/suggest that an eigenframe...
View ArticleAnswer by Ian Bush for Do xenon di- and tetrafluorides react with glass?
Firstly I'll note the title and the body of the question ask slightly different things; just because substance X doesn't react with glass doesn't mean substance X should be stored in glass.As far as I...
View ArticleAnswer by Ian Bush for Bond-order parameter $g_6(r)$
Assume we are given a configuration of atoms $\{{\bf r_i}\}$ and any other data required to characterise the atomic layout, e.g. any lattice vectors if we have periodic boundary conditions in any of...
View ArticleAnswer by Ian Bush for Are alkynes weakly polar?
Yes, alkynes can display a (small) permanent electric dipole moment, and thus are polar molecules by the usual definition. For example see https://cccbdb.nist.gov/exp2x.asp?casno=74997&charge=0...
View ArticleAnswer by Ian Bush for Why does low spin character predominate in...
This is almost a duplicate of this question. There it is shown that the Crystal Field Stabilization Energy (CFSE) is at a maximum for $\mathrm{d^6}$ ions, and low spin is strongly favoured unless there...
View ArticleAnswer by Ian Bush for How do computational programs decide how many virtual...
The basis functions you use describe a space within which your orbitals are vectors. If you have $N$ basis functions this space is $N$-dimensional, and in a $N$-dimensional space you can have at most...
View ArticleAnswer by Ian Bush for Gaussian type orbitals and p-type orbital
No, your understanding is not correct. Let the third centre at which the gaussian product is centred be $R_P$. Now we can write$$(x-x_A)=((x-x_P)-(x_A-x_P))=(x-x_P)-x_{PA}$$so defining $x_{PA}$....
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Answer by Ian Bush for What theory accurately explains metallic bonding in...
The usual MOT explanation for why the group IIA elements are metals is that the band caused by the overlap of the np orbitals is sufficiently wide to overlap that due to the ns orbitals (the one you...
View ArticleAnswer by Ian Bush for What does it mean that a state belongin to a given...
$R_x$ etc. are rotations about the indicated axis. See for example this article in chem.libretexts or this pdf
View ArticleAnswer by Ian Bush for Integral Prescreening in calculation of Electron...
The exact number saved will depend on the system size and geometry, but apart from for very small systems it will be many more than 1. Consider the two methods for a system that contain $N$ basis...
View ArticleAnswer by Ian Bush for Are there xenon compounds with two xenon atoms bonded...
One example is the $\ce{Xe2+}$ cation. Quoting from the abstract of Formation of the dixenon cation, $\ce{Xe2+}$, in fluoroantimonate(V) media by oxidation–reduction methods: spectroscopic properties...
View ArticleAnswer by Ian Bush for Virial theorem confusion
As noted in the comments I am taking the question to mean "Given there are no interparticle interactions in an ideal gas doesn't the Virial theorem predict the kinetic energy to be zero at all...
View ArticleAnswer by Ian Bush for Is cobalt (III) hexaaqua paramagnetic or diamagnetic?
Quoting Housecroft and Sharpe "Inorganic Chemistry" (second edition):The blue, low-spin $\ce{[Co(H2O)6]^3+}$ ion can be prepared in situ by ....Greenwood and Earnshaw says about $\ce {Co}^{3+}$...
View ArticleAnswer by Ian Bush for Does aluminium oxide ionize after melting point?
I'm going to try and answer a bit of confusion in the original question "Does aluminium oxide ionize after melting point?". Aluminium oxide is already ionised in the solid, or more pedantically the...
View ArticleAnswer by Ian Bush for Why don't I get a whole number when determining the...
Firstly the link you have provided unfortunately has already rotted. I suspect it was a link to a database query which disappear very rapidly. In future can you please provide a link to the original...
View ArticleAnswer by Ian Bush for If diborane has 3c-2e bonds, then why are both boron...
Well at least according to Professor William Lipscomb, who won a Nobel Prize "for his studies on the structure of boranes illuminating problems of chemical bonding", they are not electron deficient....
View ArticleAnswer by Ian Bush for What does the colon (the pairs of dots) mean in...
It represents a lone pair of electrons in a Lewis Structure.
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Answer by Ian Bush for Behavior of the Vosco-Wilk-Nusair correlation functional
A very quick google shows up https://math.nist.gov/DFTdata/atomdata/node5.html#SECTION00021200000000000000 amongst other hits - note the definition is slightly different from yours and I think you want...
View ArticleAnswer by Ian Bush for Do conformations arise from vibrations?
Yes, different conformations do arise from vibrations. And you've almost answered your own question. Conformations are different relative spatial arrangements of the atoms. Pure translations, rotations...
View ArticleComment by Ian Bush on Covalent network phase of CO2
Yes, but not totally absurd - 48GPa is appreciably less than the maximum pressure in the Earth's mantle, we're not talking supermassive black holes here.
View ArticleComment by Ian Bush on Why does Cs2SO4 have more lattice energy that Na2SO4?
Petrusevski, Vladimir & Stojanovska, Marina & Šoptrajanov, Bojan. (2007). DEMONSTRATIONS AS A TOOL FOR IRONING-OUT PRECONCEPTIONS: 1. ON THE REACTIONS OF ALKALI METAL SULFATES WITH CONCENTRATED...
View ArticleComment by Ian Bush on What is the nature of the bonds in BaO2 (Ionic or...
In a crystalline lattice it is not a good picture that ionic "bonds" occur between pairs of atoms - each ion interacts with every single other atom in the whole of the lattice, and A bonds to B picture...
View ArticleComment by Ian Bush on Why do Cr and Mn have lower enthalpy of atomisation...
It would very much help the question if you display why you think Manganese and Chromium do not follow whatever trend you are thinking about, with references to the data you use to illustrate the...
View ArticleComment by Ian Bush on Is Li2CuSb thermoelectric?
Does this make it the first, uninteresting thermoelectric? More seriously I haven't voted to close yet but I think the question could be improved by being more specific - I could throw a couple of...
View ArticleComment by Ian Bush on electronic properties simulation from experimental...
Short answer: No, it is not a good idea. The maths assume you are at a minimum, and if you don't follow the assumption you have a reasonable probability of getting unphysical results. You must optimise...
View ArticleComment by Ian Bush on Xe-F bond lengths and geometry of XeF6
What do you mean by "geometry (not shape)"? How are you differentiating the terms?
View ArticleComment by Ian Bush on Can we use formation/ cohesive energy to express the...
Stable with respect to what? The elements?
View ArticleComment by Ian Bush on Is oganesson really a noble gas?
RbXeF8 implies Xe(VII) which is very unlikely. Wikipedia, Greenwood and Earnshaw, and Housecroft and Sharpe all list MXeF$7$ and M2[XeF8], the latter stating "Cs2[XeF8] and Rb2[XeF8] are the most...
View ArticleComment by Ian Bush on Why is nitrogen dioxide brown?
Close to a nice answer,but I think this needs a bit more - why does a molecule being paramagnetic make it able to absorb light at comparatively low frequency? If paramagnetism is the cause of colour...
View ArticleComment by Ian Bush on Splitting of electronic states in Tanabe-Sugano-diagrams
Yes. The (potential) splitting is purely a reflection of the symmetry.
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